System for reduction of extraneous electrical effects



J 1933- A. H. HOTOPP, JR 1,913,551

SYSTEM FOR REDUCTION OF EXTBANEOUS ELECTRICAL EFFECTS Filed Aug. 18,1930 2 Sheets-Sheet l L 1 E- l. g c

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Aud/o frequency INVENTOR Alfred H Hozoppz/fi ATTORNEY June 13, H HQTOPPJR 1,913,551

SYSTEM FOR REDUCTION OF EXTRANEOUS ELECTRICAL EFFECTS, I

Filed Aug. 18, 1950 2 Sheets-Sheet 2 L In & P 6) 2 Curren Z Source. w:M061, r5

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0 Cbmpensalied l-Tlfer. Feceak /er f INVENTOR ATTORNEY Patented June 13,1933 UNITED STATES Amannmno'rorr, an, or CALDWELL,- NEW JERSEY, ASSIGNORTO WIRED mine, we; I or mzw YORK, n.1, A oonronarronor DELAWARE 1invention relates in general to radio trjansmittingand receiv ng systemsand speeifiqallyrelates to w red radlo systems em- It is well known in.radio totransmit and audio frequency range by means disparageai dj ethside bands, as well as bygmeaiislof a carrier and single side band.However am not aware that any system ting, over wires, thf entire audiofrequency raingefbyineansof thecarrier and one of the s id ba ds; W l if sm ti g a p e e rained portion of thesame audiofrequency range bymeansofboth side bands in order to reduce xtmmQ lS electrical effects inrec p i m I ff y Oneiot the jobjects' of my invention contransmissionand reception in which means are provided to substantially redueeextranedusnoises and electrical'effects.

ILAnothei object of my invention consists providing asystem forreduction of ex traneeus electrical effects comprisinga wiredradiobroadcasting s stem in which the carrier is transmitted togetherwith both of the side bands for a predetermined portion of thetransmission frequency range and only one of the side bands for theremainder of the transmission range with proper compensatien in thereceiver to obtain uniform reception. 4 These and other. objectsIaccomplish as hereinafter disclosed, reference beinghad to theaccompanying drawings in which:

Tis a graphical representation of a theoretical filter for transmissionof carrier and both side bands.

Figflgf'is a graphical representation of the transmission response of al ilterj usedin my invention.

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characteristics of a receiverlused in my in- F ig. 4 is aschematicrepresentation of the eleetrical organizationof one embodiments YsT mrroaBEnuorIoN or .EXTRANEOUS ELECTRICAL EFFECTS .1

L ucationmeaau ust s,1930. Serial No. 475,570., I, j,

ployingmeans to reduce extraneous electri- T59 f lq re proposed] fortransmit sists inlproducinga system for wired radio FiglBis a mphi irepresentation of'tlie in which modulated carrier frequency cnrf; rentsare impressed upon Wire lines such as" light and powerdistributionnetworks,jfit has, been found "that, that under certainconditions, extraneous modulation or; carrier will sometimes occur intheftrafis mitting medium. This extraneous: modul T tion, when itoccurs, is evidenced atthe output of the receiver by a hum which iyordi: narily composed of frequencies principally below a thousandcycles. A It is well known that devices havingfnonl linear voltagecurrent characteristics will delnodulate modulatedwaves' and that thereproduced component is twice as gre when thedevice is suppliedwithwavescorn posed of the carrierand both side than when suppliedwith'wavescompose'd of the carrier and only one side, bandL i Forexample, a space discharge detector'f tube operating on the square lawwill g'iyefa reproduced component equal to K038 cos( t+0) when carrierand'both sidebands are impressed upon it,and a reproduced componentequal to Q KU S cos (t+0) when carrier and only one side band aeimpressed upon it. It is therefore evident, then, that for a definitevalue for" carrier C andmodulation K, carrier and single'sid'e bandtransmission will require. greater-ne'- sponse in the receiver, toproducea given output, than when carrier and both side bands aretransmitted. It is therefore ob vious that the transmission andreception of carrier and both side bands is much'more satisfactory fromthe standpoint of in creased ratio of desired signal to unwanted noiseand extraneous electrical l efiects'. However, to transmit carrier andbothfside bands necessitates the use of a freqiiency 90 spacesubstantially double the freque cy width of that required for carrierand only one side band. My invention contemplates transmitting thecarrier together with beth side bands for a relatively small portion; i

the transmission frequency rangeand which extraneous modulation occurs,only one of the side bands forthe remainder of the transmissionfrequency range. 1

Fig. 1 represents the transmissioncurve lower side band is representedby f AS before stated, the extraneous or hum modulation frequencies areusually below one thousand cycles and are therefore restricted to arelatively small percent-age of the total audio frequency range. Themaximum limit of the extraneous modulation frequency for the upper sideband is represented by f in Fig.- 1, while the maximum limit fort-heextraneous frequencies for the -21. lower side band .is represented by f-The frequency range for the extreneous modulation for carrier and bothside bands is therefore represented by f -f As before pointed out, thetransmission of the carrier and both side bands effectivelyreduces, atthe receiver output, such extraneous modulations, since the ratio of thedesired signal to extraneous electrical efiects is greater fortransmission and reception of carrier together with both side bands thanfor carrier and one of the side bands for a given carrier input anddegree of signal modulation. However, the transmission of both sidebands above the extraneous modulation range is not necessary, since asatisfactory signal to noise ratio in this portion of the frequencyspectrum is obtainable with single side band transmission. Since it isof great importance to conserve space on frequency transmissionchannels, I therefore, according to my invention, produce a type offilter for both transmission and reception and which has a theoreticaltransmission curve similar to that shown in I, Fig. 2, which is evolvedfrom Fig. 1. The

upper cut-off frequency remains f as in Fig. 1, but the lower cut-offfrequenc b comes with the carrier 0 in the same re lation. The frequencyrange therefore 1 .equals f f the entire audiofrequency range beingtransmitted and received over the upper side band f c, while the lowerside band, represented by 0-f is used to transmit the audio frequencyonly over the extent of the extraneous modulation frequencies.

Fig. 4; represents a wired radio transmission and reception systememploying my invention. Light and power lines 1 extend from a light andpower current source 2.

Such light and power current source and l nes are indicative of a normalcommerc al light and power distribution network. An oscillator 3provides carrier frequency currents to the power amplifier 4. Thiscarrier frequency current is modulated by the modulator 5 under controlof a microphone 6. The modulated carrier frequency is then passedthrough filter 7 which attenuates all frequencies other than those lyingwithin the range theoretically repre sented by f ff in Fig. 2, theconstants of the filter 7 being of a value such as to pass frequencieswithin the range f f The outputfrom the filter 7 is impressed upon thelines 1 through capacitative couplings 8. A filter 9 is connectedthrough a capacitative coupling 10 to the line l. This filter 9 has atransmission response similar to that of filter 7 andwhichis graphicallydepicted in Fig. 2. The frequencies passed by filter 7 are likewisepassed by filter 9 and fed to the receiver 11. The receiver 11 has con-'stants of a value such as to produce uniform output signal level overthe entire audio frequency range thus compensating for the increasedresponse which would otherwise occur due to the transmission of carrierand both side bands for the low audio frequencies. graphicallyrepresents the characteristics of the receiver system of my invention interms of output signal level over the audio frequency range. It will benoted that the receiver is designed to be less responsive for that partof the audio frequency range transmitted by means of carrier and bothside bands than for that part of the audio frequency range transmittedby carrier and one side band. This compensation for the greater responsewhich would otherwise be present due to transmission of the'low audiofrequencies by means of carrier and both side bands produces a uniformeffective output signal level for the receiver graphically representedby the curve 0. If a receiver intended for reception of the entire audiofrequency range by means of carrier and both side bands were employed inthe system of my invention, the output signal level over the audiofrequency range would be -non-uniform as graphically represented by thecurve N. It is evident that the differences of the ordinates of thecurves 0 and M are representative of reduction in extraneous andundesirable hum and noise due to extraneous modulation of carrier. Theactual reduction of extraneous'noiseand electrical effects isrepresented by the shaded area in Fig. 3.

It will now be obvious that I have provided an effective system forsubstantially reducing the resultant hum or noise due to extraneousmodulation in the transmission and reception of modulated high frequencycurrents by employing a combination of carrier together with double sideband transmission and carrier together with single side bandtransmission with receiver response compensation. The exact circuitsReferring to Fig. 3, the curve M to be used in my system are well knownin the art, and it is also well known that the constants of thesecircuits can be adjusted to produce the results described and which incombination constitute my invention. It will, of course, be understoodthat changes can be made in my system without departing from theintended scope of my invention. I do not therefore desire to limitmyself to the foregoing except insofar as pointed out in the appendedclaims.

What I claim as new andoriginal and desire to secure by Letters Patentof the United States is:

1. A system for radio transmission comprising, a source of carriercurrent modulated at audible frequencies, means adapted to transmitcarrier and one side band of said modulated current for the entire audiofrequency range and carrier and the other side band of said modulatedcurrent for a predetermined portion of the audio frequency range inwhich extraneous modulation occurs and receiver means adapted to receivesaid transmitted current, said receiver means being adapted to produce auniform output over substantially the entire audio frequency range. i

2. A system for the reduction of extraneous electrical effectscomprising, a source of modulated high frequency current, means adaptedto transmit a predetermined portion of the audio frequency range bymeans of carrier and both side bands of said current, while transmittingthe remainder of the audio frequency range by means of said carrier andsingle side band, and receiving means adapted to receive saidtransmitted frequencies, said receiving means being less responsive tosaid carrier and double side band frequencies than to said carrier andsingle side band frequencies.

3. A hum elimination system comprising, in combination, a source of highfrequency current, means adapted to modulate said current over the audiofrequency range, means adapted to transmit carrier and both side bandsof said modulated high frequency current for a predetermined portion ofsaid audible frequency range while transmitting said carrier and singleside band for the remainder of said audible frequency range, andreceiving means adapted to receive said transmitted currents, saidreceiv ing means being less responsive to currents at frequencies withinthe range in which said carrier and both side bands are transmitted thanto currents at frequencies within the range in which said carrier andsingle side band is transmitted.

4:. In combination with a wired radio broadcasting system in whichmodulated high frequency currents are impressed upon light and powerlines, a hum elimination system comprising, a source of modulated highfrequency currents, means adapted to transmit carrier and double sidebands of said current for a predetermined part of the audio frequencyrange while transmitting carrier and single side band for the remainderof said frequency range, and receiving means, said receiving means beingless responsive to currents at frequencies within the range in whichsaid carrier and double side bands are transmitted than to currents atfrequencies within the range in which said carrier and single side bandare transmitted.

5. A system for reduction of extraneous electrical effects comprising, asource of modulated high frequency current, wire lines, means adapted totransmit over said wire lines carrier and double side bands'of saidmodulated high frequency current for a predetermined portion of theaudible frequency range while transmitting carrier and single side bandof said modulated high frequency current for the remainder of saidaudible frequency range, and receiving means for said transmittingcurrent, said receiving means being less responsive to currents atfrequencies within the range in which said carrier and double side bandsare transmitted than to currents at frequencies within the range inwhich said carrier and single side band are transmitted.

6. A system for reduction of extraneous electrical effects in accordancewith claim 4 but in which said carrier and double side bands aretransmitted over a smaller portion of the audio frequency range thansaid carrier and single side band.

7 A system for reduction of extraneous electrical effects comprising, asource of commercial light and power current, wire lines extending fromsaid source, a source of modulated high frequency current, means adaptedto impress upon said wire lines carrier and both side bands of saidmodulated high frequency current for a predetermined portion of theaudible frequency range while impressing carrier and single side bandfor the remainder of said audible frequency range, and receiving meansconnected to said wire lines and constructed to receive said impressedcurrents with substantially uniform reproduction of the audiblefrequency range.

